Nickel plating on zinc



United States Patent 3,082,156 NICKEL PLATING 0N ZINC Richard C. Brown, Muncie, Ind., assignor, by mesne usignments, to American Zinc Institute Incorporated, New York, N.Y., a corporation of New York No Drawing. Filed Aug. 19, 1960, Ser. No. 50,607

4 Claims. (Cl. 204-49) This invention relates to nickel plating, and particularly to a method and composition for electroplating nickel directly on zinc and zinc base alloys.

Plating directly on zinc and zinc base alloys with nickel strike baths of the present invention eliminates copper plating in a cyanide bath, prevents formation of a brittle intermetallic copper-zinc phase, and improves corrosion resistance of die castings, which may be further plated with nickel or chromium.

In the past, it has been customary to plate copper on zinc and zinc base alloys in a cyanide bath before applying a bright nickel plate or a chromium plate. The copper cyanide baths are toxic, and it is necessary totreat plating room wastes carefully and completely when such baths are used. This is a costly operation that the plating industry is seeking to avoid. Another disadvantage is that brittle intermetallic copper-zinc compounds are formed at ambient temperatures by diffusion between the die-cast,

zinc alloy basis metal and the copper plate. The diffusion alloying often causes blistering or peeling of the electroplate and leads to unsatisfactory appearance. The baths for the present invention are not toxic, and the nickel strike process of this invention does not cause any brittle compounds or alloys to form. The invention improves corrosion resistance and provides a very strong bond between the electroplate and the basis metal.

Various attempts to develop nickel plating baths for plating directly on zinc have been unsuccessful. Of the baths described in the prior art, one used nickel chloride, tartaric acid, and ammonium hydroxide (to adjust the pH to 5.6). Only porous, black deposits with poor covering power were obtained using this bath in the manner taught. In another bath, additions of sodium citrate, disodium, dihydrogen, ethylene-diaminetetra acetic acid, triethanol amine, sodium sulfate, and sodium hydroxide were made to nickel sulfate solutions. Only porous, cracked deposits were obtained in plating directly on zinc die castings. A nickel phosphate-phosphoric acid bath described in the literature proved to be unsuitable for plat. ing on zinc die castings. A bath containing nickel sulfate, sodium citrate, ammonium hydroxide, and sodium pyrophosphate provided a dense plate, but the plate was inferior in adherence.

The nickel plate obtained on zinc and zinc alloys with baths containing chloride or other halide ions is porous, because the halide ion tends to dissolve the zinc or alloy; and the adherence of the plate is poor. Without the halide in the conventional nickel sulfate bath, dissolution of the nickel anodes is not sufficient for satisfactorily replenishing nickel ions in the plating bath. Replacing the halide ions with fluoborate and citrate ions in accordance with the present invention, however, enables satisfactory anode dissolution and a superior plate.

Baths containing only nickel sulfate and nickel fluoborate provide deposits that are generally satisfactory ex- 3,082,156 Patented Mar. 19, 1963 citrate for a part of the nickel sulfate improves the throwing power of nickel sulfate-nickel fluoborate baths without causing the electroplate to be porous.

The table below lists preferred and useful ranges of bath compositions and operating conditions for nickel strike plating directly on zinc and zinc base alloys according to the present invention.

TABLE Preferred Range Useful Range Bath Constituents:

Ni7t l reki) Sulfate, NlSOt. 1.0 to 1.2 molar.-.. 0.5 to 1.5 molar. a

N18 1 Fluoborate, Ni- 0.2 to 0.3 molar 0.1 to 0.4 molar.

t I. Nickel Citrate, Nh- 0.07 to 0.15 molar 0.05 to 0.2 molar.

(CH|O1)t. Borio Acid, HaBOs 0.3 to 0.5 molar 0.1 molar to saturaon. pH 4.5 to 4.9 3.5 to 5.5. Operating Conditions:

Temperature 65 to F 60 to F. Cathode current dcnsity 75!? amp./sq., f :0 200 ampJsq. Work bar agitation 25 to 60 c.p.m; 2 15 to 70 c.p.n1; 1

to 4 inch stroke. to 6 inch stroke. Ai flnilaflnn Optional- Anode current density 10 to 40 amp/sq. 5 to 75 ampJsq. ft.

Voltage (between anode 4 to 7 volts 3 to 12 volts.

and cathode). Plating time 1 to 5 minutes 1 to 10 min. Plating rate 0.003 to 0.005 inch] 0.002 to 0.008 inch] hour. hour. Thickness of deposit 0.00005 to 0.00015 0.00005 to 0.0005

inch. inch.

In a typical operation of nickel strike plating on an item made of zinc or a zinc base alloy according to the present invention, the item to be plated is either buffed or electropolished, and degreased in trichloroethylene, or electropolished after degreasing. It is then cleaned conventionally either anodicaliy or cathodically, but preferably anodically, and rinsed in hot and cold water, acid dipped in 0.25 to 1.0 (weight) percent sulfuric acid solution, and rinsed in cold water. The item is then immersed in the plating bath and the work bar is started. With an appropriate DC. power supply to provide the desired current density, the circuit is closed to start electrodeposition. The plating is continued for the desired period, after which the circuit is opened, the work bar is stopped, and the plated item is removed and rinsed.

Among the advantages of the present invention are: simplicity of composition, better appearance, less porosity, better bond to basis metal, better covering in low current density areas, and less tendency to crack or flake.

The following examples show some of the advantageous results obtained with the present invention:

Example I Bufied and cleaned zinc alloy(AG40-A, also known as Zamak 3) were plated directly in an aqueous plating bath containing:

Nickel sulfate, NiSo .7H O -..molar 1.14 Nickel fl-uoborate, Ni(BF ....do 0.28 Nickel citrate, Ni (C,H O-,), do 0.08 Boric acid, HaBO; do 0.4 pH 4.91:0.2 Temperature F 74:2 Cathode current density ..amp./sq. ft-.. 100

known brighteners. In five minutes, smooth, mirror like nickel plate was deposited about 0.0003 mch thick.

Example 11 Because thicker deposits of bright nickel, i.e. 0.001 inch, or more, were brittle and showed a little cracking at edges of complex-shaped parts previously plated with 0.0001 to 0.0002 inch of nickel in the sulfate-fluoboratecitrate bath, an intermediate nickel plate was deposited prior to bright nickel, when a total nickel thickness of 0.001 inch, or more, was desired. By this procedure, zine die castings first nickel plated by the procedure of Example I were next plated with additional nickel in one of the two following solutions:

With a current density of 30 to 40 amp/sq. ft. in each case, approximately 0.0002 inch of gray nickel was deposited in 10 to 12 minutes. After rinsing, the parts next were plated with 0.0007 inch, or more, of bright nickel.

Die castings that were plated according many of the above examples showed no evidence of blistering, peeling, or delamination when they were subjected to sawing, filing, hammering, or heating (to 325 F.). Metallographic examination of cross sections likewise showed no peeling or delamination.

What is claimed is:

1. A method of electroplating comprising plating nickel on zinc and zinc base alloys from an aqueous solution 4 consisting essentially of about 0.5 to 1.5 mols per liter of nickel sulfate, about 0.1 to 0.4 mol per liter of nickel fluoborate, about 0.05 to 0.2 mol per liter of nickel citrate, and about 0.1 mol per liter to saturation of boric acid, said solution having a pH from about 3.5 to 5.5 at a cathode current density of about to 200 amperes per square foot, while maintaining the temperature of said solution between about and 85 F.

2. A composition of matter for electroplating nickel on zinc and zinc base alloys consisting of an aqueous solution consisting essentially of about 0.5 to 1.5 mols per liter of nickel sulfate, about 0.1 to 0.4 mol per liter of nickel fluoborate, about 0.05 to 0.2 mol per liter of nickel citrate, and about 0.1 mol per liter to saturation of boric acid, said solution having a pH from about 3.5 to 5.5.

3. A method of electroplating comprising plating nickel on zinc and zinc base alloys from an aqueous solution consisting essentially ofabout 1.0 to 1.2 mols per liter of nickel sulfate, about 0.2 to 0.3 mol per liter of nickel fluoborate, about 0.07 to 0.15 mol per liter of nickel citrate, and about 0.3 to 0.5 mol per liter of boric acid, said solution having a pH from about 4.5 to 4.9 at a cath. ode current density of about 75 to 125 amperes per square foot, while maintaining the temperature of said solution between about and F.

4. A composition of matter for electroplating nickel on zinc and zinc base alloys consisting of an aqueous solution consisting essentially of about 1.0 to 1.2 mols per liter of nickel sulfate, about 0.2 to 0.3 mol per liter of nickel fluoborate, about 0.07 to 0.15 mol per liter of nickel citrate, and about 0.3 to 0.5 mol'per liter of boric acid, said solution having a pH from about 4.5 to 4.9.

References Cited in the file of this patent UNITED STATES PATENTS Atkinson Oct. 10, 1961 

1. A METHOD OF ELECTROPLATING COMPRISING PLATING NICKEL ON ZINC AND ZINC BASE ALLOYS FROM AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF ABOUT 0.5 TO 1.5 MOLS PER LITER OF NICKEL SULFATE, ABOUT 0.1 TO 0.4 MOL PER LITER OF NICKEL FLUOBORATE, ABOUT 0.05 TO 0.2 MOL PER LITER OF NICKEL CITRATE, AND ABOUT 0.1 MOL PER LITER TO SATURATION OF BORIC ACID, SAID SOLUTION HAVING A PH FROM ABOUT 3.5 TO 5.5 AT A CATHODE CURRENT DENSITY OF ABOUT 50 TO 200 AMPERES PER SQUARE FOOT, WHILE MAINTAINING THE TEMPERATURE OF SAID SOLUTION BETWEEN ABOUT 60 AND 85*F. 